Nacelles are well known in the aviation industry as streamlined enclosures for aircraft engines. Each enclosure ordinarily includes one or more perforated face sheets which are intended to absorb engine noise and provide structural support for the engine. Moreover, the perforated face sheets can be comprised of composite laminates. These composite laminates are beneficial because they are substantially light in weight, resistant to fatigue in sonic environments, and have favorable life cycle costs.
The perforation of the sheets typically requires that uncured laminate sheets are forced onto a pinmat. The typical pinmat is comprised of a series of pins integrally formed within a thick mat portion.
These pinmats ordinarily are formed by a multiple step process. This process normally begins with the injection molding of the pinmat utilizing a talc-filled polypropylene material. However, various other materials and manufacturing processes can be utilized as desired. Thereafter, a milling machine typically is utilized for trimming the edges of the pinmat and removing specific pins therefrom. The removal of specific pins allows the pinmat to leave predetermined portions of the face sheet unperforated as desired. The milling machine includes a milling head with a one-piece end mill chucked therein. The end mill normally is intended to operate at a specific predetermined height for the purpose of shearing specific pins at their bases at the surface of the pinmat.
However, the one-piece end mill typically cuts the pins either too high or too low because the predetermined height does not account for the variations in the thickness of the mat portion, as well as for the imperfections in the flatness of the machine bed. Specifically, variations in the thickness of the mat portion can be up to 0.010 inches or higher. Additionally, the imperfections in the flatness of the machine bed can create height fluctuations up to 0.002 inches, as well. These variations and imperfections typically prevent the milling machine from shearing the pins off at the surface of the mat. For example, if the milling machine is operated at a height below the surface of the pinmat, the end mill can create nubs, pits, or grooves within the surface and deposit friction melted debris thereon. On the other hand, if the milling machine is operated at a height above the surface, the end mill can produce pin nubs extending from the surface of the pinmat. Typically, either result requires an operator to smooth and repair the surface using a hand-held scraper or an orbital sander.
A drawback of the nubs and pits created by existing shaving mechanisms is that the smoothing operation for repairing the pinmat usually requires a substantial amount of time thereby increasing the overall manufacturing cycle time and the costs associated therewith.
Another drawback of the nubs and pits created by existing shaving mechanisms is that the hand finishing operation can result in fatigue and repetitive-motion injuries, i.e. carpel tunnel syndrome, to the operators.
Therefore, a need exists for a shaving mechanism that removes pins from a pinmat without leaving a nub, a pit, or a groove within the surface of the pinmat.